Tachometer



Jan. 7, 1941. a H, s n' 2,228,090

TACHQMETER Filed Jan. 18. 1939 Two Phase I Generator WITNESSES' INVENTOR $.40. I I w Patented Jan. 7 1941 UNITED V STATES PATENT OFFICE 2,22s,o 9u TACHOMETER Pennsylvania Application January 1a, 1939, Serial No. 251,554

13 Claims. This invention relates to tachometers, and it has particular relation to tachometers for measuring both the direction and rate of rotation of bodies. In my copending application, Serial No; 212,439, filed June 8, 1938, I have disclosed a high output inductor generator particularly suited for-ta-' chometers. When only the rate of rotation of a body is to be measured, this generator may be connected to a suttable instrument in a manner well known in the art. However, some applications of tachometers require that, in addition to In accordance with my invention, a polyphase generator-is employedfor measuring both rate and direction of rotation of a body. In a specific embodiment of my invention, a two-phase, three-wire generator is provided with a rectifier for each phase. The outputs ofthe rectifiers are connected in opposition to a center zero indicating instrument. By placing an impedance,

such as a capacitive reactance or condenser, in

the common lead of the three-wire, two-phase generator, the polarity of the direct currents applied to the indicating instrument will depend on the direction of rotation of the generator, and

the magnitude of the direct-current voltage applied to the instrument will depend upon the rate of rotation of the generators It is, therefore, an object of my invention to provide a simple tachometer installation for measuring both the rate and direction of rotation of a It is another object of my invention to provide a tachometer for measuring both the rate and direction of rotation of a body-which requires only two conductors for supplying energy to anindicatingdnstrument. v

- It is a furtherobject of my invention to provide a two-phase generator with means for varying the relative outputs of the two phases in accordance with the direction of rotation of the generator.

' Other objects of my invention will be apparent from the following description taken in conjunction with the accompanyingdrawing, in which the single figure is a diagrammatic view'or a tachometer embodying my invention.

Referring to the drawing, I have illustrated a rotatable shaft I, the rate.and'direction-of retation of which are to be measured. For this purpose, a'generator 1 is coupled in any suitable manner to'the shaft l for rotation in accordance. with the rotation of the shaft. Although I 5 may employ various types of polyphase generators, I prefer to employ a two-phase generator of the high output type disclosed in my aforesaid application. This generator is of the two-phase, three-wire type, the phasewi'ndings 10 being depicted on the drawing as coils A and B; Each of the phases A and B is connected across the input terminals 3, 4 and 5, 6 of\ an independent rectifler I, 8. These rectiflers may be of thecopper oxide contact type and are illustrated lb as full-wave rectiflers. However; it-is to beunderstood that any other suitable rectifier knownto the art may be employed. If desired, theserectifiers may be provided with filters for smoothing the direct-current outputs thereof in a man- 20 ner known to the art: The voltage applied to drawing, terminals 9 and II being positive, and

terminals lb and I2 being negative. Energy for an indicating instrument is is obtained from the series circuit through a of taps IG and I'I on the resistors which are connected to the 35 instrument through apair of conductors l8 and I9. Although the indicating instrument may be. of any typeknown to the'art, I prefer to. employ a sensitive DArsonval type of instrument having a center zero. Afiillustrzited, the instrument 40 I5 is provided with markings R and F for denoting respectively Reverseie and Forward rota-. tion of the shaft l..

An impedance 20 is inserted in the common lea'd of the three-wire generator for providing 45 an output of the generator that'is dependent upon the direction and rotation of the shaft I.

Although an inductive impedance may beem-v lployed, I prefer a capacitive reactance or .con denser as illustrated.

rectifier 8 is equal to the voltage supplied be-' tween phase B of the generator less the voltage drop across thecapacitive reactance 20. Since the generator is provided with two phases, it follows that according to the direction of rotation thereof, either phase A or phase B may provide a leading voltage. That is, if for clockwise rotation of the generator, the voltage across phase A leads the voltage across phase B by 90 electrical degrees, then for counter-clockwise rotation of the generator the voltage across phase B leads the voltage across phase A by 90 electrical degrees.

The voltage drop'across the capacitive reactance 20 is not symmetrical with respect to the two phase voltages of phases A and B. For that reason, the voltages across the inputs to the rectifiers I and 8 will be dissimilar. Furthermore, this dissimilarity is reversible in accordance with the direction of rotation of the generator for the reason that the relationship of the voltages across the phases A and B reverses with reversal of the direction of rotation of the generator.

This may be illustrated more specifically by assuming a clockwise rotation of the generator. In this case, the voltage across the phase A leads the voltage across the phase B by 90 degrees. Under the assumed conditions, the vector resultant of the voltage across the phase A and the voltage drop across the impedance 20 is larger than the resultant of the voltage drop across the phase B and the voltage drop across the impedance 20. Consequently, the input voltage to the rectifier 1 will be larger than the input voltage to the rectifier 8, and the larger voltage of the rectifier I controls the indication of the instrument I5. If the rotation of the generator reverses because of reversal of rotation of the shaft I, the voltage across the phase B now leads the voltage across the phase Aiby 90 electrical degrees, and the resultant voltage applied to the input terminals of the rectifier 8 will be greater than that applied to the input terminals of the rectifier 1. Therefore, the direct-current output of the rectifier 8 controls the indication of the instrument I5.

Since the polarities of the rectifiers I and 8 rectifier I exceeds that of the rectifier 8, the

quently, the degree of deflection of the pointer of the instrument is a measure of the rate of rotation of the generator and may be calibrated to represent the rotation of the shaft I in revolutions per minute or any other desired unit,

The installation and operation of the complete tachometer designed in accordance with my invention may be briefly recapitulated: A

I two-phase generator iscoupled for rotation from 1 a shaft I, the rotation of which is to be measured.

'Ihe rectifiers I and 8 together with the associated resistors i3 and I4 and the capacitive reactance 28 all may be placed in the generator frame or adjacent thereto. This means that the only wiring required between the rotating shaft and the indicating instrument I5 is represented by two conductors and I9, one of which may, of course, be replaced by ground in certain installations. More than one instrument may be connected to the conductors l8 and I9 either in series or in parallel as desired.

Because of the capacitive reactance 20, a voltage will be applied to the rectifier I, which will be larger or smaller than the voltage applied to the rectifier 8, in accordance with the direction of rotation of the generator. The difference between these voltages will vary in accordance with the rate of rotation of the generator in etiher direction. If the voltage applied to the rectifier I is smaller than that applied to the rectifier 8, current will flow from the tap ll to the conductor I9 through the instrument l5, conductor l8, and tap l8. If the voltage applied to the rectifier 1 is smaller than that applied to the rectifier 8, indicating reversal of the direction of rotation of the generator, current will then flow from the tap [6 through the conductor I8, instrument 'l5, conductor I9, back to the tap II; that is, the direction of current flow through the conductors l8 and I9 and the instrument I5 is dependent upon the direction of rotation of the generator. This direction of flow represents one variable characteristic controlled by the direction of rotation of the shaft I.

A second variable characteristic of the energy applied to the conductors I8, I9 is that of magnitude which is controlled by the difference between the voltages applied to the rectifiers 1 and8, and this difference in turn is'afunction of the rate of rotation of the generator. These two variables determine the direction of rotation of the pointer of the instrument l5 and the magnitude of deflection thereof. Therefore, the position of the pointer indicates completely the condition of rotation of the shaft l. 7

Although I have described my invention with reference to. certain specific embodiments thereof, it is obvious that various modifications thereof are possible. Therefore, I do not wish my invention to be restricted except as required by the appended claims when interpreted in view of the priorart.

I claim as my invention:

1. In an electrical device for measuring the speed and direction of rotation of a rotating body, a source of alternating current having a first characteristic varying in accordance with the speed of rotation of said body in either direction, and having a second characteristic varying in accordance with the direction of rotation of said body, a direct-current measuring instrument having a pair of input terminals,'and means the output of said polyphase generator for supplying direct current energy having a polarity varying in accordance with the direction of rotation of said rotatable element to said conductors. 3. In an electrical measuring device responsive etc the rotation of a reversible rotating body, a polyphase generator having a rotatable element mounted for rotation in accordance with rotation of said body, means for varying the magnitude ratio of the voltages supplied by two phases of said generator'in accordance with the direction of rotation of said rotatable-element, and measuring means responsive to said ratio.

4. In a supply system, a two-phase generator having a rotatable element, a lead common to both phases, a load across each of said phases, and means in said common lead for varying the proportion of a characteristic of the energy supplied by the phases of said generator in accordance with the direction of rotation of said generator.

5. In a measuring system, a first source of alternating current, a second source 0! alternating current, a rectifier unit for each of said sources, an eiectro-responsive device connected to said rectifier units, said rectifier units being opposed relative to said electro-responsive device, and

means for varying the difference between a characteristic oi the outputs from said sources in accordance with a predetermined variable.

6. In a measuring system, a two-phase generator having a terminal common to both phases and an additional terminal for each phase, a reactance, a lead connected to said common terminal through said reactance, and an electro-re-. sponsive device controlled by the ratio' oi. the outputs between said lead and each of said additiona1 terminals. 1

'7. In a measuring system, a two-phase generator having a terminal common to both phases,

and an additional terminal for each phase, a capacitance, a lead connected to said common terminal through said capacitance, a pair of rectifier units, eachrectifler unit being energized in accordance with the output between said lead and a separate one of said additional terminals, connections for connecting the outputs of said rectifiers in series, said connections including resistance means, and an electro-responsive device energized from said series connected rectifiers through said resistance means.

8. In a tachometer, a three-wire, two-phase inductor generator, a rectifier connected across each of said phases a capacitance in the lead common to both of the phases of said generator, said rectifiers having their outputs connected in an additive series circuit, a direct-current responsi'veinstrument connected across said series circuit, and impedance means in said series circuit between said instrument connection and each 01 said rectifiers.

9. In an electrical device responsive to the rotation 01' a rotating body, direct current translating means, and energizing means for supplying to said direct current translating means a direct current quantity having a polarity varying in accordance with the direction of rotation of said rotating'body, said energizing means including a source of alternating current having an output controlled by the rotation of said rotating body, and means for deriving from said output said direct current quantity for energizing said direct current translating means.

10. In an electrical device responsive to the rotation of a rotating body, direct current translating means, and energizing means for supply ing to said direct current translating means a direct current quantity having a polarity varying in accordance with the direction of rotation of said rotating body, and having a magnitude varying in accordance with the rate of rotation of said rotating body, said energizing means including a source of alternating current having an output controlled by the direction and rate of rotation of said rotating body, and rectifying means for converting said output into said direct current quantity.

11. In an electrical device responsive to the rotation of a rotating body, a rotatable polyphase generator, means ior.varying the ratio of the voltage magnitudes .oi' separate phases of said polyphase generator in accordance with the direction of rotation of said polyphase generator, means for rectifying the outputs of said separate phases into direct current quantities, and translating means controlled by said direct current quantities. 1

12. In an electrical device responsive to the rotation of a rotating body, a rotatable polyphase generator, means for varying the ratio of the voltage magnitudes of separate phases of said polyphase generator in accordance with the direction of rotation of said p lyphase'generator, means for rectifying the outputs oi said separate phases into direct current quantities, and translating means controlled by said direct current quantities, said tranflating means including indicating means controlled by the difference in magnitudes oi said direct current quantities and controlled by the polarity of the predominating direct current quantity, the polarities 01' said direct current quantities diflering relative to said BENJAMIN n. SMITH. 

